The invention relates to a method of making iron or steel in a very low slag process utilizing petroleum coke as a fuel to produce the molten iron or steel preproducts and reduction gas in a melter gasifier.
Petroleum coke is a product of refinery operations and is produced in the United States utilizing three types of coke processing technology. Specifically these technologies as known to one skilled in the art are delayed, fluid and flexi. By far most petroleum coke in the United States is produced using delayed technology. In 1990, according to the U.S. Department of Energy, 55 refineries in the United States which had coking facilities and a refinery capacity of 8 million barrels per day produced slightly over 76,000 short tons per day of petroleum coke. The residual petroleum coke produced amounted to about 6% by weight of each barrel of crude oil processed by the refineries.
Petroleum coke is generally the bottom end of refinery operations after most of the light ends and oils have been recovered from the original crude. The make up of petroleum coke will vary depending on a number of factors including the crude being processed and the process being utilized. Generally on a dry basis petroleum coke will be composed largely (approximately 90%) of fixed carbon and typically include sulfur (0.05% to 6%) and nitrogen (2% to 4%). Various metals typically including vanadium, iron and nickel are found in petroleum coke. Usually, a typical petroleum coke contains about 10% volatile matter. Petroleum coke contains up to 10 to 15% moisture before drying.
Petroleum coke is produced either as blocky sponge coke or needle coke from delayed cokers or in a shot size form from fluid bed cokers. Sponge coke from delayed cokers is by far the most important coke produced in the United States. Calcined sponge coke is used primarily in the manufacture of graphite electrodes, anodes and shaped products. Approximately one-third of the sponge coke production is used in these products.
Until recent years the remainder of the petroleum coke in the U.S. was used as fuel for power plants and cement kilns. However due to the high sulfur content, the need for blending with coal to maintain ignition and flame stability and environmental problems , petroleum coke has become less suitable as a boiler fuel. The high sulfur content of petroleum coke also poses problems for cement kilns. Excess sulfur will cause finished concrete to expand and crack and also influences setting time. The high vanadium content also poses problems with refractories. Thus there is a substantial amount of excess petroleum coke which must be disposed. The high sulfur content and the relatively high amounts of metals such as vanadium and nickel make such disposal a real environmental problem which the present invention is directed to solving.
U.S. Pat. No. 4,849,015 to Fassbinder et al. discloses a method for two-stage melt reduction of iron ore, in which iron ore is pre-reduced substantially to wustite and at the same time melted down in a melting cyclone, and then liquid hot metal is produced in an iron bath reactor connected to the outlet of the melting cyclone and receiving the melted wustite by adding carbonaceous fuels and oxidizing gas to the melt. The resulting reaction gas from the melt is afterburned, and the dust-laden, partly burned reaction gases from the iron bath reactor are accelerated and further afterburned by adding a hot blast with a temperature of 800.degree. C. to 1500.degree. C., and at least a portion of such accelerated, after burned reaction gases are introduced into the melting cyclone to reduce and melt fresh iron ore.
Carbonaceous fuels, such as coke, carbonized lignite, petroleum coke, etc., but preferably coal of varying quality, are fed to the melt in the iron bath reactor. Slag-forming additives, such as lime, fluorspar, etc., are also fed to the iron melt to set the desired slag composition. Although it is irrelevant for the present invention whether these substances are introduced into the melt on the bath surface or from below the bath surface, it is preferable to add them through underbath feed nozzles.
U.S. Pat. No. 4,806,158 to Hirsch et al. discloses a process for the production of reduced iron oxide-containing materials. Iron oxide and solid carbonaceous reducing agent are charged into a first expanded fluidized bed, which is supplied with an oxygen-containing fluidizing gas. The gas residence time selected is controlled in the reactor containing the first fluidized bed so that the reduction potential will result in a reduction of the iron oxide material not in excess of the FeO stage. A gas-solids suspension discharged from the first fluidized bed is supplied to a second expanded fluidized bed, which is supplied with a strongly reducing fluidizing gas. Strongly reducing gas and a major portion of the resulting devolatilized carbonaceous material are discharged from the upper portion of the second fluidized bed. Reduced material having a metallization of 50 to 80% and the remaining devolatilized carbonaceous material are discharged from the lower portion of the second fluidized bed. Suitable carbonaceous materials include all coals, from anthracite to lignite, carbonaceous minerals and waste products, such as oil shale, petroleum coke or washery refuse, provided that they are solid at room temperature. The oxygen-containing gas preferably consists of oxygen or of oxygen-enriched air.
U.S. Pat. No. 4,897,179 to Mori et al. provides a method of producing reduced iron and light oil from iron ore and heavy oil which comprises a thermal cracking step of subjecting heavy oil to thermal cracking while retaining iron ore particles in a fluidized state to produce light oil and simultaneously to deposit coke as by-product on the surface of the iron ore particles; a gasification step of putting the coke-deposited ore in contact with an oxidizing gas including steam and oxygen in a fluidized state to react the coke with the gas thereby to produce a reducing gas containing hydrogen and carbon monoxide and of heating the coke-deposited ore upward of a reduction temperature of iron ore by partial oxidization of the coke; and a reduction step of reducing the coke-deposited iron ore in a fluidized state by the reducing gas to produce reduced iron. When the gasification step is performed by an oxidizing gas containing a majority of steam and up to 15 vol. %, based on the steam, of oxygen at 800.degree.-1000.degree. C. under a pressure of 0-10 kg/cm.sup.2 G, a reducing gas containing high-concentration hydrogen gas is obtained.
In recent years methods utilizing a melter gasifier have been developed to produce molten iron or steel preproducts and reduction gas. Most of these processes utilize a coal fluidized-bed. A high temperature is produced in the melter gasifier utilizing coal and blown in oxygen to produce a fluidized bed and iron sponge particles are added from above to react in the bed to produce the molten iron.
Thus in European Patent B1-0010627, a coal fluidized-bed with a high-temperature zone in the lower region is produced in a melter gasifier, to which iron sponge particles are added from above. On account of the impact pressure and buoyancy forces in the coal fluidized-bed, iron sponge particles having sizes greater than 3 mm are considerably braked and substantially elevated in temperature by the heat exchange with the fluidized bed. They impinge on the slag layer forming immediately below the high-temperature zone at a reduced speed and are melted on or in the same. The maximum melting performance of the melter gasifier, and thus the amount and temperature of the molten iron produced, not only depends on the geometric dimensions of the melter gasifier, but also are determined to a large extent by the quality of the coal used and by the portion of larger particles in the iron sponge added. When using low-grade coal, the heat supply to the slag bath, and thus the melting performance for the iron sponge particles, decline accordingly. In particular, with a large portion of iron sponge particles having grain sizes of about 3 mm, which cannot be heated to the same extent as smaller particles by the coal fluidized-bed when braked in their fall and which, therefore, necessitate a higher melting performance in the region of the slag layer, the reduced melting performance has adverse effects in case low-grade coal is used.
A melter gasifier is an advantageous method for producing molten iron or steel preproducts and reduction gas are described in U.S. Pat. No. 4,588,437. Thus there is disclosed a method and a melter gasifier for producing molten iron or steel preproducts and reduction gas. A first fluidized-bed zone is formed by coke particles, with a heavy motion of the particles, above a first blow-in plane by the addition of coal and by blowing in oxygen-containing gas. Iron sponge particles and/or pre-reduced iron ore particles with a substantial portion of particle sizes of more than 3 mm are added to the first fluidized-bed zone from above. A melter gasifier for carrying out the method is formed by a refractorily lined vessel having openings for the addition of coal and ferrous material, openings for the emergence of the reduction gases produced, and openings for tapping the metal melt and the slag. Pipes or nozzles for injection of gases including oxygen enter into the melter gasifier above the slag level at least two different heights.
Another process utilizing a melter gasifier is described in U.S. Pat. No. 4,725,308. Thus there is disclosed a process for the production of molten iron or of steel preproducts from particulate ferrous material as well as for the production of reduction gas in the melter gasifier. A fluidized-bed zone is formed by coke particles upon the addition of coal and by blowing in oxygen-containing gas by nozzle pipes penetrating the wall of the melter gasifier. The ferrous material to be reduced is introduced into the fluidized bed. In order to be able to produce molten iron and liquid steel preproducts in a direct reduction process with a lower sulfur content of the coal used, the ferrous material to be reduced is supplied closely above the blow-in gas nozzle plane producing the fluidized bed. An arrangement for carrying out the process includes a melter gasifier in which charging pipes penetrating its wall are provided in the region of the fluidized-bed zone closely above the plane formed by the nozzle pipes. The ferrous material to be melted as well as the dusts separated from the reduction gas and, if desired, fluxes containing calcium oxide, magnesium oxide, calcium carbonate and/or magnesium carbonate are introduced therethrough.
There is also a process known as the COREX.RTM. process (COREX.RTM. is a trademark of Deutsche Voest-Alpine Industrieanlagenbau GMBH and Voest-Alpine Industrieanlagenbau). This process is described in Skilling's Mining Review, Jan. 14, 1989 on pages 20-27. In the COREX.RTM. process the metallurgical work is carried out in two process reactors: the reduction furnace and the melter gasifier. Using non-coking coals and iron bearing materials such as lump ore, pellets or sinter, hot metal is produced with blast furnace quality. Passing through a pressure lock system, coal enters the dome of the melter gasifier where destructive distillation of the coal takes place at temperatures in the range of 1,100.degree.-1,150.degree. C. Oxygen blown into the melter gasifier produces a coke bed from the introduced coal and results in a reduction gas consisting of 95% CO+H.sub.2 and approximately 2% CO.sub.2. This gas exits the melter gasifier and is dedusted and cooled to the desired reduction temperature between 800.degree. and 850.degree. C. The gas is then used to reduce lump ores, pellets or sinter in the reduction furnace to sponge iron having an average degree of metallization above 90%. The sponge iron is extracted from the reduction furnace using a specially designed screw conveyor and drops into the melter gasifier where it melts to the hot metal. As in the blast furnace, limestone adjusts the basicity of the slag to ensure sulfur removal from the hot metal. Depending on the iron ores used, SiO.sub.2 may also be charged into the system to adjust the chemical composition and viscosity of the slag. Tapping procedure and temperature as well as the hot metal composition are otherwise exactly the same as in a blast furnace. The top gas of the reduction furnace has a net calorific value of about 7,000 KJ/Nm.sup.3 and can be used for a wide variety of purposes.
The fuels used in these processes are typically described as a wide variety of coals and are not limited to a small range of coking coal. The above noted article from Skilling's Mining Review, notes that petroleum coke suits the requirements of the COREX.RTM. process. Brown coal and steam coal which are relatively poor quality coal having a relatively high ash content i.e. plus 15%, have been identified as suitable for use in these processes. Coke made from coal has also been identified as a fuel for many of the processes utilizing melter gasifiers.
The present invention is directed to a solution for the disposal of an environmentally objectionable material and provision of a new and unexpectedly superior fuel source for processes utilizing melter gasifiers to make molten iron or steel preproducts in a process which results in very low slag formation.